25 research outputs found
Lateral transport of domains in anionic lipid bilayer membranes under DC electric fields: A coarse-grained molecular dynamics study
Dynamic lateral transport of lipids, proteins, and self-assembled structures
in biomembranes plays crucial roles in diverse cellular processes. In this
study, we perform a coarse-grained molecular dynamics simulation on a vesicle
composed of a binary mixture of neutral and anionic lipids to investigate the
lateral transport of individual lipid molecules and the self-assembled lipid
domains upon an applied direct current (DC) electric field. Under the potential
force of the electric field, a phase-separated domain rich in the anionic
lipids is trapped in the opposite direction of the electric field. The
subsequent reversal of the electric field induces the unidirectional domain
motion. During the domain motion, the domain size remains constant, but a
considerable amount of the anionic lipids is exchanged between the
anionic-lipid-rich domain and the surrounding bulk. While the speed of the
domain motion (collective lipid motion) shows a significant positive
correlation with the electric field strength, the exchange of anionic lipids
between the domain and bulk (individual lipid motion) exhibits no clear
correlation with the field strength. The mean velocity field of the lipids
surrounding the domain displays a two-dimensional (2D) source dipole. We
revealed that the balance between the potential force of the applied electric
field and the quasi-2D hydrodynamic frictional force well explains the
dependence of the domain motions on the electric-field strengths. The present
results provide insight into the hierarchical dynamic responses of
self-assembled lipid domains to the applied electric field and contribute to
controlling the lateral transportation of lipids and membrane inclusions.Comment: 9 pages, 6 figure
Coupling between pore formation and phase separation in charged lipid membranes
We investigated the effect of charge on the membrane morphology of giant
unilamellar vesicles (GUVs) composed of various mixtures containing charged
lipids. We observed the membrane morphologies by fluorescent and confocal laser
microscopy in lipid mixtures consisting of a neutral unsaturated lipid
[dioleoylphosphatidylcholine (DOPC)], a neutral saturated lipid
[dipalmitoylphosphatidylcholine (DPPC)], a charged unsaturated lipid
[dioleoylphosphatidylglycerol (DOPG)], a charged saturated
lipid [dipalmitoylphosphatidylglycerol (DPPG)], and
cholesterol (Chol). In binary mixtures of neutral DOPC/DPPC and charged
DOPC/DPPG, spherical vesicles were formed. On the other
hand, pore formation was often observed with GUVs consisting of
DOPG and DPPC. In a DPPC/DPPG/Chol
ternary mixture, pore-formed vesicles were also frequently observed. The
percentage of pore-formed vesicles increased with the DPPG
concentration. Moreover, when the head group charges of charged lipids were
screened by the addition of salt, pore-formed vesicles were suppressed in both
the binary and ternary charged lipid mixtures. We discuss the mechanisms of
pore formation in charged lipid mixtures and the relationship between phase
separation and the membrane morphology. Finally, we reproduce the results seen
in experimental systems by using coarse-grained molecular dynamics simulations.Comment: 34 pages, 10 figure
Charge-induced phase separation in lipid membranes
The phase separation in lipid bilayers that include negatively charged lipids
is examined experimentally. We observed phase-separated structures and
determined the membrane miscibility temperatures in several binary and ternary
lipid mixtures of unsaturated neutral lipid, dioleoylphosphatidylcholine
(DOPC), saturated neutral lipid, dipalmitoylphosphatidylcholine (DPPC),
unsaturated charged lipid, dioleoylphosphatidylglycerol
(DOPG), saturated charged lipid,
dipalmitoylphosphatidylglycerol (DPPG), and cholesterol.
In binary mixtures of saturated and unsaturated charged lipids, the combination
of the charged head with the saturation of hydrocarbon tail is a dominant
factor for the stability of membrane phase separation.
DPPG enhances phase separation, while
DOPG suppresses it. Furthermore, the addition of
DPPG to a binary mixture of DPPC/cholesterol induces phase
separation between DPPG-rich and cholesterol-rich phases.
This indicates that cholesterol localization depends strongly on the electric
charge on the hydrophilic head group rather than on the ordering of the
hydrocarbon tails. Finally, when DPPG was added to a
neutral ternary system of DOPC/DPPC/Cholesterol (a conventional model of
membrane rafts), a three-phase coexistence was produced. We conclude by
discussing some qualitative features of the phase behaviour in charged
membranes using a free energy approach.Comment: 17 pages, 6 figure
33. Transition between lamellar and micellar phases in surfactant solutions(poster presentation,Soft Matter as Structured Materials)
この論文は国立情報学研究所の電子図書館事業により電子化されました
両親媒性分子が形成する階層的秩序構造
京都大学0048新制・課程博士博士(理学)甲第15849号理博第3590号新制||理||1524(附属図書館)28428京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 吉川 研一, 教授 太田 隆夫, 教授 小貫 明学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA
Nano-domain formation in charged membranes: Beyond the Debye-Hückel approximation
We investigate the microphase separation in a membrane composed of charged lipids, by taking into account explicitly the electrostatic potential and the ion densities in the surrounding solvent. While the overall (membrane and solvent) charge neutrality is assumed, the membrane can have a non-zero net charge. The static structure factor in the homogeneous state is analytically obtained without using the Debye-Hückel approximation and is found to have a peak at an intermediate wave number. For a binary membrane composed of anionic and neutral lipids, the characteristic wave number corresponds to a scale from several to tens of nanometers. Our numerical calculation further predicts the existence of nano-domains in charged membranes